As we were checking transformers and vaults for the cause of the outage, the other Lineman opened a vault lid…
My response…
“Yeah, that’s most likely not it, we better keep looking”
Laughter ensued…
I got a call about an outage in an area that is pretty new. About 5-6 years old. It’s all underground cable carrying 14,400 volts. First thought was someone smashed into a pad mounted transformer or something. No construction is going on so nobody would have dug into it…??? One Lineman headed to go start checking transformers from the end of the line and I headed to the circuit breaker. Sure enough it was open. Knocking out power to about 150 apartments, a grocery store, and a big laundromat.
After the smoke cleared from the vault my partner had opened we found this…
Believe it or not, it was our lucky day. This is what is called a “Radial”. Meaning the underground power line doesn’t loop around back to itself. In a loop you have 2 possible directions to feed electricity to the customers. On a Radial you only have one feed. Loops are the best in all honestly.
The reason I say we lucked out is because the cable that went bad was the one that feeds the laundromat and not the cable that feeds both the laundromat and the grocery story store.
We quickly isolated the section of bad cable, then energized all the apartments and grocery store. They were only out of power for about 1/2 hour. The laundromat on the other hand is gonna be out for a little while.
As you can see the explosion was pretty violent. It blew a hole in the bottom of the elbow splice, blew the cable tag off, and bunt off a bleeder wire.
After isolating the cable to be working on and installing our protective grounds, we started into repairing it.
That’s not suppose to do that??!!
After removing the elbow from the cable, I think we found the issue. It had a bit of a blow out wouldn’t you say??
I’m really surprised the people living in the house 50 feet away didn’t come out and say anything about the explosion and smoke.
I’ve seen a handful of these failures but not one that happened at the bottom of the pressed connector and the insulation.
Normally it’s a breakdown of the insulation and a pin hole develops. Then the electricity goes through the insulation to the copper concentric neutral wires or ground. This one was pretty odd since it was only 5-6 years old.
Cut the bad piece of cable off and splice on a new elbow… simple as that. By the time we got everything back on it had only been 1-1/2 hours. It helps to be able to carry the necessary items on my truck to make quick repairs like this.
After getting all the meters on, we took a better look at the cable. Lineman always want to play Sherlock Holmes on stuff like this. Our conclusion, judging by the shape of the insulation, is that when this elbow was spliced the insulation was contaminated or dirty. The insulation had a flat spot that kind of spiraled down the side. The electricity from the lug tracked down the insulation until it hit the ground wires.
Red=insulationBlue=electricity
That’s our conclusion anyway as to why this 14,400 volt elbow blew up. Sorry no selfies and what not, we were super busy at the time. One day I will show you Hivers how this cable is spliced.
I try my best to show people things that happen whenever your lights go out. Us lineman don’t just go and flip a switch….
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